I can't identify that fort either, which is frustrating because I feel i should know it, but in searching for clues I came across a fantastic website that I'm sure many people know well, but for the laggards like me its...
Radfan and the Hawker Hunter
Enjoy!
BTW I could not find that picture on that website, but there are a lot and I could easily have missed it. It certainly should be there, I'm thinking.